There are a number of known processes for forming plastics materials into the required shapes for making relatively small articles, such as injection molding, but such processes become progressively more unwieldy, and the associated equipment becomes much more expensive, when it is required to make relatively large panels such as building panels suitable for use as partitions, for example.
It is known to produce composite panels based on fibrous materials by forming a fiber layer or mat and then applying outer layers of expandable phenol resin and hot-pressing the assembly to consolidate it. Such a method of forming boards is described in U.S. Pat. No. 4,734,231 (Morita et al). JP2003112329 discloses a similar kind of board comprising a core of mixed carbon material and phenol resin powder, and a surface material comprising mixed solid phenol resin and chaff or straw, which is formed by compressing the mixtures and heating to cross-link the phenol resin. However, panels including such fibrous materials may not be sufficiently dense or strong for general building or construction purposes, and it is also difficult to achieve a smooth finish on the outer surface.
Furthermore, if it is desired to utilize ground-up recycled waste material (for example) to make a more solid core, it is difficult to make a strong integral structure without employing a multi-stage process in which the core material is first combined with a binding material. This is because the thermoplastic material of the outer layer may not penetrate the core layer sufficiently to bind it together.
It is also known to make structural panels from molded material, by separately forming relatively thin panels from a first, more fine grained material so as to provide a relatively well finished “skin”, and then arranging a pair of the relatively thin panels in a suitable mold or former, with a space between them in which another plastics material is formed into a foam, so as to provide a composite structure which is relatively strong, and may also be relatively coarse grained or contain a large volume of voids, so as to provide the resulting composite structure with good insulating qualities.
As an alternative to plastics or molded materials for the external skins, of course, sheets of metal or other suitable sheet material may be utilized, but in any case the formation of such panels by conventional methods tends to involve a relatively slow and cumbersome multi-stage process, because of the necessity to pre-form some components and then to manipulate them into the required arrangement for forming the final structure. Where it is required to manufacture relatively large structural panels, for instance, sizes such as 2.4 m×1.2 m, it is consequently expensive to automate such known systems because of the need for complex handing equipment.
Accordingly, a need exists for alternative systems for forming aggregate materials from heat fusable powdered materials.